A general discussion of the production of inertial fusion targets by use of glass microspheres is contained in an article titled "Producing Hollow Glass Microspheres for Inertial Fusion Targets" published by Lawrence Livermore National Laboratory in a report titled "Laser Fusion--Book 2," May 1980, pages 40 through 48. The same report has a discussion of single-shell and double-shell targets in an article titled "Heavy-Ion-Driven Fusion" at pages 50 through 57 and a discussion of coatings for such targets in an article titled "Ultrasmooth Coatings for Microsphere Targets" at pages 78 through 83. Another article titled "Density Diagnosis of Fusion Targets by Neutron Activation" published in this report at pages 30 through 38 discusses the limitations of existing targets and the shifting emphasis to more ablatively driven targets.
Multishell designs of targets are currently being explored in an effort to provide greater control of the ablative reactions required in order to fully utilize longer and more powerful pulses to ultimately implode the central fuel materials in the targets.
A discussion of the production of multishell targets is contained in a paper titled "Fabrication of Multishell Laser Fusion Target" by Farnum and Fries, submitted to a meeting of the Plasma Physics Division of the American Physical Society in San Francisco, Calif., on November 15-19, 1976. This paper discusses the desirability of multishell targets to the attainment of improved efficiency and correspondingly higher yields while accomplishing thermonuclear burn by the use of lower energy laser beams. The paper discusses the production of a multishell target with an outer shell assembled from hemispheres glued together and supporting the fuel pellet by a crosshair support made of two glass fibers. Alternatively, it states that support can be provided by mounting a fuel-filled microballoon on thin plastic films. The described outer shells are produced by coating a hemispherically shaped mandrel with plastic and leaching the mandrel in acid. The plastic hemispheres are then assembled with the crosshair supports for the inner fuel pellet. They are glued at their mating equator surfaces to complete the spherical outer shell.
The requirements of shell sphericity and uniformity in multishell targets are very stringent (within limits of less than 1%). The present invention has arisen from an effort to produce a multishell target in which the outer shell structures have no surface imperfections due to hemispherical seams. Surface irregularities in the assembly may not exceed approximately 200 Angstroms. Gross flaws such as might be caused by inclusion of seams or joint regions in the shell are intolerable in the production of targets meeting these requirements.